This study is being conducted to determine the optimal dose of autologous CART-19 T cells engineered to express anti-CD19 chimeric antigen receptors in patients with relapsed or refractory CD19 positive chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). The two dose levels being assessed are 1-5x10e8 versus 1-5x10e7. The trial will be conducted in two stages. In stage I subjects will be randomized into one of the two dose cohort with a1:1 ratio for a total of 12 subjects per dose cohort. Stage II will be to enroll an additional 8 subjects to the selected dose cohort once safety, tolerability and clinical responses have been evaluated to determine the optimal dose cohort.